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A319500 a(n) is the least m for which A006987(n) = binomial(m,k) for some k, 2 <= k <= m/2.

%I A319500 #14 Sep 21 2018 22:37:26
%S A319500 4,5,6,6,7,8,7,9,10,11,8,12,8,13,9,14,15,10,9,17,18,11,19,20,10,12,22,
%T A319500 10,23,24,13,25,26,11,27,14,28,29,30,15,11,31,12,32,33,16,34,35,36,37,
%U A319500 17,38,13,39,40,12,18,41,42,43,12,44,19,45,14,46,47,48,20,49,50,51,13,52,21,15,53
%N A319500 a(n) is the least m for which A006987(n) = binomial(m,k) for some k, 2 <= k <= m/2.
%C A319500 First differs from A022911 at n=18.
%H A319500 Robert Israel, <a href="/A319500/b319500.txt">Table of n, a(n) for n = 1..10000</a>
%F A319500 A006987(n) = binomial(a(n),A318955(n)).
%e A319500 a(3) = 6 because A006987(3) = 15 = binomial(6,2).
%p A319500 N:= 10000: # for binomial(n, k) values <= N
%p A319500 S:= {}:
%p A319500 for n from 2 while n*(n-1)/2 <= N do
%p A319500   for k from 2 to n/2 do
%p A319500     v:= binomial(n, k);
%p A319500     if v > N then break fi;
%p A319500     if not member(v,S) then
%p A319500       S:= S union {v};
%p A319500       M[v]:= n;
%p A319500     fi
%p A319500 od od:
%p A319500 A006987:= sort(convert(S,list)):
%p A319500 seq(M[A006987[i]],i=1..nops(A006987));
%Y A319500 Cf. A006987, A022911, A318955.
%K A319500 nonn
%O A319500 1,1
%A A319500 _Robert Israel_, Sep 20 2018